The continuous shrinking in dimensions of electronic devices utilized in ultra large scale integrated (ULSI) circuits in recent years has resulted in increasing the resistance of the interconnect metallization as well as increasing the capacitance of the intralayer and interlayer dielectric. This combined effect increases signal delays in ULSI electronic devices. In order to improve the switching performance of future ULSI circuits, low dielectric constant (k) insulators, and particularly those with a dielectric constant significantly lower than silicon oxide, are needed to reduce the capacitance.
Most of the fabrication steps of very large scale integration (“VLSI”) and ULSI chips are carried out by plasma enhanced chemical or physical vapor deposition techniques. The ability to fabricate a low k dielectric by a plasma enhanced chemical vapor deposition (PECVD) technique using previously installed and available processing equipment simplifies its integration in the manufacturing process, reduces manufacturing cost, and creates less hazardous waste. U.S. Pat. Nos. 6,147,009 and 6,497,963 assigned to the common assignee of the present invention, which are incorporated herein by reference in their entirety, describe a low dielectric constant material consisting of elements of Si, C, O and H atoms having a dielectric constant not more than 3.6 and which exhibits very low crack propagation velocities. Such low k dielectrics are also referred to as C doped oxides or organosilicate glass (OSG).
U.S. Pat. Nos. 6,312,793, 6,441,491 and 6,479,110 B2, assigned to the common assignee of the present invention and incorporated herein by reference in their entirety, describe a multiphase low k dielectric material that consists of a matrix composed of elements of Si, C, O and H atoms, a phase composed mainly of C and H and having a dielectric constant of not more than 3.2.
U.S. Patent Application Publication Nos. 2005/0156285 A1 and 2005/0245096 A1, assigned to the common assignee of the present invention, and incorporated herein by reference in their entirety, describe means for improving the stability and/or physical properties such as tensile strength, elastic modulus, hardness cohesive strength and crack velocity in water of SiCOH dielectric materials.
U.S. Patent Application Publication Nos. 2005/0194619 A1 and 2006/0165891 A, assigned to the common assignee of the present invention and incorporated herein by reference in their entirety, provide a low dielectric material with increased cohesive strength that includes atoms of Si, C, O and H, in which a fraction of the C atoms are bonded as Si—CH3 functional groups and another fraction of the C atoms are bonded as Si—R—Si, wherein R is phenyl, —(CH2)n— where n is greater than or equal to one, HC═CH, C═CH2, C≡C or a [S]n linkage wherein n is as defined above.
For porous SiCOH (“p-SiCOH”) dielectrics, post treatment in oxidizing ambients (including, for example, oxygen and water) increases the film's stress by increasing the formation of tetrahedral strain. The increased tetrahedral strain is caused by increased Si—O—Si bonding in the p-SiCOH dielectric film. The formation of Si—O—Si bonding is increased in such dielectric films by the presence of Si—OH and Si—H bonding in the as-deposited film or after performing a high-energy (including, for example, ultra-violet (UV), electron-beam (E-beam) and/or thermal) post deposition treatment step.
Thermodynamically, Si—OH and Si—H bonds in p-SiCOH films are readily oxidized by oxygen and water in an ambient to form Si—O—Si bonding due to a low activation energy needed for the formation of such Si—O—Si bonding. As p-SiCOH dielectrics become more porous with lower k values, the surface area and the absorption of oxygen/water increase significantly and become more susceptible to oxidation thus forming an increased number of strained Si—O—Si bonds to be present in the dielectric film. The formation of Si—O—Si bonds, in turn, increases the film's stress and crack velocity to levels which are not acceptable in semiconductor interconnect structures.
In view of the above, there is a need for providing a p-SiCOH dielectric film in which the film's stress and crack velocity are not significantly increased as compared to prior art p-SiCOH dielectrics. That is, a p-SiCOH dielectric film is needed in which the content of Si—O—Si bonding in the film is decreased by decreasing the content of Si—OH and Si—H bonding in the p-SiCOH dielectric film.